This invention relates generally to apparatus for use in well completions in wells where it is undesirable to put excess pressure on the well bore caused by lowering the casing into the well bore.
In the process of drilling a well it becomes necessary to stabilize the borehole from collapse of its walls, to set well casing in the well bore and to fix it in place by cementing it in place. The well may then be drilled further, or the completion process to begin hydrocarbon production may be carried out.
In vertical or horizontal boreholes, or sections of a well having vertical and horizontal boreholes, one or more casing strings are lowered into the hole and are anchored therein by a column of cement placed in the annulus between the casing string and the wall of the borehole. It has become conventional practice to fill the casing string with heavy drilling fluid or mud which prevents the increasing subterranean pressure from crushing inwardly, or collapsing, the casing string as it is lowered, or floated, into the well bore. When the string has been placed at the desired depth, being held at the surface or placed on a hanger from a previously set casing string of larger diameter, a wiper plug is launched into the casing string and oil well cement is added to the string above the wiper plug. Pressure pumping apparatus at the surface is used to pump the mud, and then the cement out of the lower end of the string and past a float shoe, or well tool having a back pressure valve, at its lower end and into the casing/well bore annulus. It should be mentioned that if the back pressure valve or float shoe is located at the bottom end of the casing string it is referred to as a float shoe. If this device is used interiorly to the length of a full casing string, it is referred to as a float collar. The difference in the use of this type of device as a shoe or a collar is merely whether it is threaded to the casing on one end (shoe), or on both ends (collar).
When the wiper plug lands on the float shoe, increased pumping pressure is used to burst or rupture a frangible diaphragm across the interior of the wiper plug and to permit the cement to go into the annulus, which was above the wiper plug. The back pressure valve in the float shoe prevents the cement placed in the annulus from simply re-entering the casing into any cement ports above the valve. In any case, when the desired amount of cement has been pumped into the annulus and has set, a drilling tool is lowered into the casing string and used to drill out the plug (or plugs) and the float shoe containing the back pressure valve. This opens the lower end of the casing string for further completion operations or drilling.
Some float shoes having mud jets, or directed openings, facing downwardly have been used for assisting lowering of casing into place by providing downwardly directed mud jets during the casing run in to assist circulating out any rock xe2x80x9ccuttingsxe2x80x9d present in the uncased section of borehole.
The downwardly facing jets assist in moving any remaining rock xe2x80x9ccuttingsxe2x80x9d in the well bore to be circulated out of the well via the annulus between the casing and borehole wall during the run in operation. Some such tools used as float shoes have had upwardly facing fluid ports or jets to assist in the distribution of cement into the borehole/casing annulus once the tool is in place. No known float shoes having both types of fluid ports or jets have been used.
In the use of this type of float shoe, one or more back pressure valves (or one way valves) are positioned by cementing them into a short piece of pipe threaded to the end (when used as a shoe) or to a section between casing lengths (when used as a collar) of the casing string. These check valves prevent the re-entry of cement or mud interiorly to the casing during the run in and cementing operation. A float shoe or collar of this type can have other possible valve configurations. Such valves can be configured to only act as check valves when xe2x80x9cactivatedxe2x80x9d such as by running in an activation tool or pumping an activation tool or an obscuration ball down the casing string from the surface.
Downwardly facing ports or jets are useful during casing run in. Upwardly facing jets promote the equal circumferential distribution of cement when cementing takes place. The upwardly facing jets create turbulence in the casing/borehole annulus and this tends to promote desired circumferential distribution of cement about the annulus.
It is apparent from the foregoing that it would be highly desirable in optimizing the run in and cementing operation that a float shoe or float collar having jets directed in a downward direction during the run in, and then having jets directed only in an upward direction during the cementing operation, would make such an operation much safer, more economical, and more efficient. The float shoe/collar apparatus of the present invention provides just such a reliable, safe and economical system.
The apparatus of the present invention comprises a float shoe (or which could be used as a collar) that incorporates a check valve, or a plurality of such valves, which can allow the casing to fill up from the bottom with well fluid (auto fill) during run in. Below the valve, or valves, is a center outlet hole as well as both upwardly and downwardly facing jets. A tube inside the float shoe holds the flapper (or check) valve(s) mechanism open to allow fluid into the casing. This same tube also covers and closes a set of upwardly facing jets during run in. The downwardly facing jets are open to aid in washing the borehole wall during the casing run in or float in. Once the casing string has reached the desired depth, an obscuration ball or a tool is pumped down the casing. The ball seats in the float shoe tube. With an increase in pumping pressure from the surface, the seated ball then causes the float shoe tube to move downwardly inside the tool. The downward movement allows the check valve(s) (or flappers) to swing closed, thus activating the check valve(s). When the tube shifts downwardly it closes and shuts off the downwardly facing jets and exposes, or opens, the upwardly facing jets to assist in cement distribution, during the cementing operation, to all sides of the casing.
The invention may be best understood by reference to the detailed description thereof which follows and by reference to the appended drawings. The drawings are intended to be illustrative of the preferred embodiment of the invention but are not intended to be limitative of the invention as it may admit to more than one embodiment. It is to be understood that the valves in the float shoe and valves in the float collar may be the same.